Cadophora bubakii (Laxa) Damm & S.Bien, 2020

Bien, Steffen & Damm, Ulrike, 2020, Arboricolonus simplex gen. et sp. nov. and novelties in Cadophora, Minutiella and Proliferodiscus from Prunus wood in Germany, MycoKeys 63, pp. 119-161 : 119

Cadophora bubakii (Laxa) Damm & S.Bien comb. nov. Figures 5C , 8

Margarinomyces bubakii Laxa, Zentbl. Bakt. ParasitKde, Abt. II 81: 392. 1930. (Basionym)

≡ Phialophora bubakii (Laxa) Schol-Schwarz, Persoonia 6 (1): 66. 1970.

Type.

Czech Republic, Prague, from a margarine factory, margarine, O. Laxa leg., collection date unknown (isolated by O. Laxa, deposited in CBS collection by O. Laxa probably 1930), CBS H-491, CBS H-7316, GLM-F117482 - isotypes; CBS 198.30 = IMI 24000 = NCTC 3273 = VKM F-162 = LM 288 = LM 793 = GLMC 1895 - culture ex-isotype.

Description.

Sexual morph not observed. Asexual morph on SNA. Vegetative mycelium hyaline, smooth-walled, septate, branched, 1-3 µm wide, sometimes becoming brown with age, chlamydospores absent. Sporulation abundant, conidia formed on hyphal cells. Conidiophores hyaline, smooth-walled, occasionally with acropleurogenous branching, up to 26 µm long. Conidiogenous cells enteroblastic, hyaline, smooth-walled, discrete conidiogenous cells cylindrical to navicular, often slightly inflated having a flask-shaped appearance, often constricted at the base, 3-12 × 1.5-3.5 µm, necks cylindrical, 1-2.5 × 1-2 µm, collarettes distinct, cylindrical to funnel-shaped, 0.5-1 µm long, 1-1.5 µm wide at the upper edge, opening 1-1.5 µm wide, periclinal thickening observed. Conidia aggregated in heads, hyaline, smooth-walled, aseptate, subglobose to ellipsoidal or cylindrical with both ends rounded, straight or slightly curved, (2-)2.5-4.5(-6) × 1.5-2 µm, mean ± SD = 3.6 ± 0.9 × 1.7 ± 0.2 µm, L/W ratio = 2.1.

Culture characteristics.

Colonies on SNA flat with an entire to undulate margin, white, lacking aerial mycelium, reverse same colour, 36-56 mm diam. in 2 wk (25 °C in the dark); Colonies on OA flat with an entire to undulate margin, olivaceous to olivaceous black, sometimes covered by floccose aerial mycelium, olivaceous grey, reverse same colours, 24-27 mm diam. in 2 wk (25 °C in the dark).

Notes.

The genus Margarinomyces was described 1930 with Ma. bubakii as type species after causing problems in a margarine factory in Czech Republic by forming greenish-black spots on and in margarine cubes that smelled like bitter-almond (benzaldehyde) ( Laxa 1930). The fungus was shown to survive 20 min at 60 °C and to be resistant to organic preservatives such as sodium benzoate that was, however, only tolerated in margarine up to a concentration of 0.2% ( Laxa 1930). According to the CBS website, strain CBS 198.30 is ex-isotype of Ma. bubakii . Schol-Schwarz (1970) included Ma. bubakii in Phialophora and considered C. obscura as a synonym. The genus Margarinomyces had been included in Phialophora by Gams and McGinnis (1983), though excluded by Cole and Kendrick (1973), but Ma. bubakii has never been considered as a species of Cadophora before. All nine Margarinomyces species had been combined in other genera, most of them in Coniochaeta (http://www.indexfungorum.org).

Cadophora bubakii (strain CBS 198.30) differs from C. obscura (strain CBS 269.33) by forming conidiogenous cells that are often slightly inflated and therefore flask-shaped, while those of CBS 269.33 are mostly narrow cylindrical. Conidia of strain CBS 198.30 are sometimes subglobose and, on average, distinctly shorter than the ellipsoidal to cylindrical conidia of CBS 269.33. Moreover, colonies of CBS 198.30 grow faster. Van Beyma (1943) compared Ma. bubakii and Ph. obscura and mentioned flask-shaped conidiogenous cells and a faster colony growth rate of Ma. bubakii and narrow phialides of Ph. obscura as well. However, the conidia shape of both species was described and illustrated as rod-shaped.

The ITS sequences of the two C. bubakii strains included in the phylogeny of this study, CBS 198.30 and CBS 837.69, are identical but differ both in 19 nucleotides from that of the C. obscura strain CBS 269.33. The EF-1α sequence of the two species differs in 31 nucleotides. The TUB sequences of CBS 198.30 and CBS 269.33 were not able to be aligned with each other and the rest of the dataset and therefore excluded from the phylogeny.

A blastn search with the ITS sequence of CBS 198.30 resulted in high similarities (99.82% and 99.64%) with " Ph. bubakii " strains CBS 837.69 (included in our analysis) and CBS 836.69, both isolated from margarine, as well as CBS 834.69, isolated from wood pulp of Populus tremula ( Vu et al. 2019).

Figures

Figure 5. Colony surface of analysed strains on OA medium. A Arboricolonus simplex GLMC 459 T B Cadophora africana CBS 120890 T C C. bubakii CBS 198.30 T D C. luteo-olivacea GLMC 1264 E C. novi-eboraci GLMC 1472 F C. obscura CBS 269.33 G C. prunicola CBS 120891 T H C. prunicola GLMC 1633 I C. ramosa GLMC 377 T J Minutiella pruni-avium GLMC 1624 T K Proliferodiscus ingens GLMC 1751 T L Proliferodiscus sp. GLMC 460. Cultures A, J-L after 4 wk. Cultures B-I after 2 wk. Strains with a superscript T are ex-type cultures.

Figure 8. Cadophora bubakii comb. nov. A-H conidiophores and conidiogenous cells (arrows indicate short necks) I conidia A-I from SNA A-I LM. Scale bar: 5 μm (A applies to H-I).